Simple spool rewinder to make it easier to transfer filament from one spool to another. The design is self tightening when you run a drill. An embedded nut means you won't strip the plastic. You will need a 1/4 - 20 tap.If you print version 2, you won't need to pause to insert the nut. I haven't printed that version. If you print version 3, you need to pause at 39.5 mm height, insert nut, and then continue.